Conventionally, a reduction layout print function is known as a function of a copying machine, which reads a plurality of documents, lays them out on one paper sheet, and prints them. According to this function, for example, four A4 documents can be read, reduced, laid out on one A4 paper sheet, and output (so-called 4-in-1).
In executing the reduction layout print function, the copying machine reduces a read A4 document to A6 and temporarily saves the reduced document in a storage device such as an internal memory. After the read of four A4 documents and reduction to A6 are completed, the four A6 documents saved in the memory are laid out on an A4 paper sheet and printed.
For example, a monochrome copying machine which reads and prints a document in monochrome requires a memory capacity of about 2 MB to implement 4-in-1 (when an A4 document is reduced to A6, the data amount per monochrome binary image data in A6 size for 400 dpi is about 500 KB, and the capacity is about 2 MB for four documents).
However, as the resolution and gray scale of color image data increase, the amount of image data processed by a color multifunction peripheral (to be referred to as an MFP hereinafter) is growing, and as a result, the necessary memory capacity is also increasing. For example, to implement the above-described 4-in-1 by storing four A6 documents in a memory, the data amount per color multilevel image data in A6 size for 600 dpi is about 25 KB, and the memory capacity must be about 100 MB for four documents. If such an MFP is to be implemented, the cost increases because of the use of the 100-MB memory. In addition, the image transfer rate and processing speed between processing modules in the MFP become low along with the increase in image data amount. As a result, the processing speed and performance of the device decrease.
To prevent this, a method is available in which read image data of each page is compressed and saved to decrease the memory capacity required for each document. For example, assume that the memory capacity assigned to each document is 1 MB. In this case, when each document image data is JPEG-compressed to 1 MB, the memory capacity can be decreased as indicated below.
TABLE 1Compression InformationData Amount Afterof Compression ParameterCompressionDocument 11/251 MBDocument 21/301 MBDocument 31/201 MBDocument 41/101 MB
The compression information of the compression parameter in Table 1 is based on document 1 (25 B). A 1/25 compression parameter indicates that document 1 (25 MB) can be compressed to 1 MB. A 1/10 compression parameter indicates that document 1 (25 MB) can be compressed to 2.5 MB. The amount of image data of document 4 (100 MB) can be compressed to 1 MB by using the 1/10 compression parameter. This indicates that document 4 contains frequency components less than document 1, i.e., document 4 contains a large amount of blank region. Hence, even when the 1/10 compression parameter as a low compression parameter is used as compared to document 1, document is compressed to 1 MB. That is, the 1/10 compression parameter indicates low compression (high image quality). The compression rate rises in the order of 1/20 compression parameter, 1/25 compression parameter, and 1/30 compression parameter. That is, the 1/30 compression parameter indicates highest compression (low image quality).
As described above, when compression is executed such that the data amount falls within the target memory capacity, the amount of high-resolution color image data can be reduced, and the problems of cost and performance can be solved. When compression is executed by changing the compression parameter for each image data such that the data amount falls within the target memory capacity, the degradation in image quality by compression can be minimized.
However, when a plurality of image data compressed by different compression parameters are to be laid out as image data of one page by 4-in-1 and printed, or the image data laid out are to be transmitted by using the Internet or a public line network, the plurality of image data compressed by different compression parameters must be compressed again (recompressed) as image data of one page by using one compression parameter.
The reasons are as follows. First, when the plurality of image data are to be recompressed by their compression parameters, eight different compression parameters must be prepared at maximum per page for 4-in-1 (Since images of four pages are laid out in one page, four different compression parameters are used. In addition, since one compression parameter includes a pair of parameters for luminance component and color difference component, four pages×two kinds=eight kinds of compression parameters are necessary at maximum). For 16-in-1, 32 different compression parameters must be prepared at maximum per page (Similarly, 32 kinds of compression parameters are necessary at maximum because each of 16 pages uses two kinds of compression parameters). In addition, a mechanism to compress and hold image data in each area by using the plurality of kinds of compression parameters must be prepared. This increases the load in MFP hardware design, and the cost of MFP inevitably rises.
Second, to transmit data by using the Internet or a public line network, transfer data between MFPs, or make MFPs cooperate, the image data receiving side must have a mechanism capable of decoding the plurality of kinds of different compression parameters. If such a mechanism is not present, received image data can be neither browsed nor printed, and the convenience for users is poor.
In the conventional MFP, when image data of one page is to be recompressed by using one compression parameter, a compression parameter for highest compression is selected from the compression parameters of the plurality of image data contained in the image data of one page. For this reason, the printed image data of one page contains considerably degraded image data.